1. Technical Field
The present disclosure relates to a lighting system, especially to a lighting system having interlaced driving mechanism.
2. Description of the Prior Art
Flat panel displays (FPDs) are widely used displays nowadays. Because FPDs have slim shapes, low power dissipation and low radiation, FPDs are widely applied on mobile electronic devices as monitors, cell phones, notebooks, televisions and PDAs (personal digital assistants). When operating an FPD, the transmittances of the pixels are adjusted by utilizing a backlight module, so that the FPD can display images accordingly. Thus, the backlight module is a key element for operating an FPD. Please refer to FIG. 1, FIG. 1 shows a related art lighting system 100 operated as a backlight module. As depicted in FIG. 1, the lighting system 100 includes a plurality of power driving units 111-112, a plurality of lighting units 121-124, a circuit board 170 and a plurality of current control units 191-194. For reducing the length of wires and simplifying the circuit layout of the lighting system 100, the lighting units 121-124 are configured sequentially on the circuit board 170. That is, the lighting unit 122 is configured between the lighting units 121 and 123, and the lighting unit 123 is configured between the lighting units 122 and 124. The first power driving unit 111 is electrically connected to the neighboring lighting units 121 and 122, and the second power driving unit 112 is electrically connected to the neighboring lighting units 123 and 124. The first power driving unit 111 is used to provide the first sub-current Id1 to the first lighting unit 121 and provide the second sub-current Id2 to the second lighting unit 122. The first current Ip1 is the combined current of the first sub-current Id1 and the second sub-current Id2. The second power driving unit 112 is used to provide the third sub-current Id3 to the third lighting unit 123 and provide the fourth sub-current Id4 to the fourth lighting unit 124. The second current Ip2 is the combined current of the third sub-current Id3 and the fourth sub-current Id4. The first to fourth current control units 191-194 are electrically connected to the first to fourth lighting units 121-124 to control the first to fourth sub-currents Id1-Id4 respectively.
Please refer to FIG. 2, FIG. 2 shows the waveforms of signals for operating the lighting system 100 of FIG. 1. The horizontal axis represents time. In FIG. 2, waveforms of the first sub-current Id1, the second sub-current Id2, the third sub-current Id3, the fourth sub-current Id4, the first current Ip1 and the second current Ip2 are shown from top to bottom. As depicted in FIG. 2, the phase difference of two successive currents of the first sub-current Id1 to the fourth sub-current Id4 is 90 degrees. During period T11, because the levels of the first sub-current Id1 and the second sub-current Id2 are both at a turn-on level Ion, the level of the first current Ip1 equals to 2Ion. Thus, the output power of the first power driving unit 111 equals to the first power voltage Vp1 multiplied by 2Ion. Similarly, during period T12, because the levels of the third sub-current Id3 and the fourth sub-current Id4 are both at the turn-on level Ion, the level of the second current Ip2 equals to 2Ion. Thus, the output power of the second power driving unit 112 equals to the second power voltage Vp2 multiplied by 2Ion. Therefore, the rated power of the first power driving unit 111 must exceed 2Ion×Vp1, and the rated power of the second power driving unit 112 must exceed 2Ion×Vp2. Besides, when operating a stereoscopic display device to perform three-dimensional (3D) images for each eye of a user to receive different images, in order to avoid reducing the brightness of images, the brightness of the light outputted from a backlight module is usually doubled. Please refer to FIG. 3, FIG. 3 shows the waveforms of signals for operating the lighting system of FIG. 1 to drive a stereoscopic display device. The horizontal axis represents time. As depicted in FIG. 3, when the variation range of levels of the first sub-current Id1 and the second sub-current Id2 are both doubled to 2Ion, the variation range of the level of the first current will reach 4Ion, thus the output power of the first power driving unit 111 must exceed 4Ion×Vp1. Similarly, the output power of the second power driving unit 112 must exceed 4Ion×Vp2. Therefore, the manufacturing cost is raised and the design complexity is heightened.
Please refer to FIG. 4, FIG. 4 shows another related art lighting system 200 operated as a backlight module. As shown in FIG. 4, the lighting system 200 includes a plurality of power driving units 211-212, a plurality of lighting units 221-226, a circuit board 270 and a plurality of current control units 291-296. The lighting units 221-226 are configured on the circuit board 270 sequentially. For reducing the length of traces and simplifying the circuit layout of the lighting system 200, the first power driving unit 211 is electrically connected to the first to third lighting units 221-223. The second power driving unit 212 is electrically connected to the fourth to sixth lighting units 224-226. The first power driving unit 211 is used to provide the first sub-current Id1 to the first lighting unit 221, the second sub-current Id2 to the second lighting unit 222 and the third sub-current Id3 to the third lighting unit 223. The first current Ip1 is the combined current of the first sub-current Id1, the second sub-current Id2 and the third sub-current Id3. The second power driving unit 212 is used to provide the fourth sub-current Id4 to the fourth lighting unit 224, the fifth sub-current Id5 to the fifth lighting unit 225 and the sixth sub-current Id6 to the sixth lighting unit 226. The second current Ip2 is the combined current of the fourth sub-current Id4, the fifth sub-current Id5 and the sixth sub-current Id6. The first to sixth current control units 291-296 are electrically connected to the first to sixth lighting units 221-226 to control the first to sixth sub-currents Id1-Id6 respectively.
Please refer to FIG. 5, FIG. 5 shows the waveforms of signals for operating the lighting system 200 of FIG. 1. The horizontal axis represents time. In FIG. 5, waveforms of the first sub-current Id1, the second sub-current Id2, the third sub-current Id3, the fourth sub-current Id4, the fifth sub-current Id5, the sixth sub-current Id6, the first current Ip1 and the second current Ip2 are shown from top to bottom. As depicted in FIG. 5, the phase difference between two successive currents of the first sub-current Id1 to the sixth sub-current Id6 is 60 degree. During period T21, because the levels of the first sub-current Id1, the second sub-current Id2 and the third sub-current Id3 are all at a turn-on level Ion, the level of the first current Ip1 equals to 3Ion. Thus, the output power of the first power driving unit 211 equals to the first power voltage Vp1 multiplied by 3Ion. Similarly, during period T22, because the levels of the fourth sub-current Id4, the fifth sub-current Id5 and the sixth sub-current Id6 are all at the turn-on level Ion, the level of the second current Ip2 equals to 3Ion. Thus, the output power of the second power driving unit 212 equals to the second power voltage Vp2 multiplied by 3Ion. Therefore, the rated power of the first power driving unit 211 must exceed 3Ion×Vp1, and the rated power of the second power driving unit 212 must exceed 3Ion×Vp2. Besides, when operating a stereoscopic display device to perform three-dimensional (3D) images for each eye of a user to receive different images, in order to avoid reducing the brightness of images, the brightness of the light outputted from a backlight module is usually doubled. When the variation range of levels of the first sub-current Id1, the second sub-current Id2 and the third sub-current Id3 are all doubled to 2Ion, the variation range of the level of the first current will reach 6Ion, thus the output power of the first power driving unit 211 must exceed 6Ion×Vp1. Similarly, the output power of the second power driving unit 112 must exceed 6Ion×Vp2. Therefore, the manufacturing cost is raised and the design complexity is heightened.